Modified water-borne alkyd resins have been described in EP 0 758 365 B1. In this document, high gloss topcoats are disclosed that are made in a two-step reaction, the first step being a radically initiated copolymerisation of unsaturated fatty acids, meth(acrylate) monomers having polyoxyalkylene groups, and methacrylic acid in mixture with further olefinically unsaturated monomers, and the second step being a condensation reaction of the modified fatty acids together with further (unmodified) unsaturated fatty acids, multifunctional alcohols having from two to six hydroxyl groups, aromatic and/or aliphatic dicarboxylic acids, and optionally, cyclic or polycyclic carboxylic acids. The mandatory use of meth(acrylate) monomers having polyoxyalkylene groups as comonomers does away with the need to add solvents to achieve high gloss, but may impair the water and humidity resistance due to the hydrophilic properties of these comonomers.
Further modified alkyd resins have been described in DE 31 32 937 A1. These modified alkyd resins are made from a water-dilutable alkyd resin dispersion having an acid number of from 5 mg/g to 40 mg/g, a hydroxyl number of from 150 mg/g to 300 mg/g, and a mass fraction of solids of from 30% to 90%. Acrylic and methacrylic monomers including also acid functional and hydroxy-functional monomers together with radical initiators and chain transfer agents are added to the heated dispersion, and the mixture is subjected to polymerisation. Crosslinking is effected by addition of etherified melamine formaldehyde resins.
Other modified water-borne alkyd resins have been described, i.a., in U.S. Pat. No. 5,538,760 A. In the process described therein, an alkyd resin is dissolved in one or more monoethylenically unsaturated monomers to form a mixture, the said alkyd resin being prepared in a separate step from a saturated fatty acid having from six to twenty-four carbon atoms, a diol component selected from the group consisting of cycloaliphatic diols having from six to twenty carbon atoms and aliphatic diols having from three to twenty carbon atoms, a dicarboxylic acid selected from the group consisting of aromatic dicarboxylic acids having eight to fourteen carbon atoms, aliphatic dicarboxylic acids having from four to twelve carbon atoms, and cycloaliphatic dicarboxylic acids having from eight to twelve carbon atoms, and the mixture is dispersed in water in the presence of a surfactant to form an emulsion which is subsequently heated upon addition of a radical initiator to effect a polymerisation reaction leading to formation of a latex. The mass fraction of the alkyd resin in the aqueous emulsion before polymerisation in the examples fall into a range of from 0.131 kg/kg (example 5) to 0.264 kg/kg (Example 16). Higher mass fractions have not been described, nor exemplified. The acid numbers of the alkyd resins used range from 1.47 mg/g (alkyd resin A) to 3.12 mg/g (alkyd resin E). No higher acid numbers have been described or reported in the examples. The mass ratio of alkyd resin to ethylenically unsaturated monomers is between 1:0.66 (example 16) to 1:2.3 (examples 4 and 5). Higher mass ratios are reported to form no stable latices (examples 2 and 3).
The latices described are used for cleaning hard surfaces such as concrete, tiles, wood, formica, metal, glass, or ceramic, and to provide them with a protective shine.
It has been found in the experiments underlying the present invention that the low ratio of the mass of alkyd resin and the mass of polymer derived from the ethylenically unsaturated monomers limits the gloss of such coating made from latices have these two constituents in a unfavourable way.
It was therefore an object of this invention to provide an alkyd resin system with a high mass fraction of solids that forms a stable aqueous emulsion, that can be made by external emulsification from an alkyd resin that is dispersible in water with a higher mass fraction of solids, and that provides a fast drying coating with high gloss surfaces.